PALEOCLIMATE AND PALEOENVIRONMENTAL INTERPRETATIONS OF THE LATE PLEISTOCENE COLUMBIAN MAMMOTH REMAINS FROM WACO MAMMOTH NATIONAL MONUMENT, WACO, TX

The Waco Mammoth National Monument (WMNM) is a significant paleontological site situated near the confluence of the Brazos and Bosque Rivers in Waco, TX, that preserves the remains of approximately eighteen Columbian mammoths (Mammuthus columbi) and several other late Pleistocene species. Previous studies have proposed two fundamentally different scenarios to explain the high density of mammoth remains and the potential causes behind their mass mortality at the site: (1) the death and deposition of mammoth remains was caused by a dramatic episode of incision and rapid burial or (2) the mammoth fossil represent an attritional assemblage that died due to a prolonged drought. This study assesses these scenarios by presenting data from a composite stratigraphic section from inside the dig shelter at WMNM, that encompasses the in-situ fossil layers. Our stratigraphic sequence is ~3.5 m thick and contains at least three discrete mammoth fossil-bearing intervals. Particle size analyses indicate a very high clay content with multiple sand lenses interspersed within a fining-upwards succession throughout the section. Chemical index of alteration values suggests intermediate weathering through the entire profile, and paleosol macromorphology indicates of seasonal precipitation and relatively minimal pedogenesis in the paleosol horizons. Paleosol-transfer function estimates of mean annual precipitation (MAP) indicate a semi-arid to dry, sub-humid climate regime. Taken together, our preliminary results show that the mammoth assemblage could not have been deposited in a single, dramatic episode of incision. Instead, it demonstrates that the mammoth remains at WMNM were deposited in at least three discrete intervals on a distal flood plain in a semi-arid to dry, sub-humid climate. These results support the interpretation that WMNM is an attritional assemblage that accumulated in an interval of prolonged drought. Further analyses will focus on refining these paleoclimate interpretations.